The invention relates to the papermaking art and, in particular, to the manufacture of paper products having basis weights above about 80 pounds per 3000 square feet up to and including about 300 pounds per 3000 square feet, such as file folders, non-corrugated containers, and the like, which exhibit improved properties for office environments and long term storage.
Heavy weight cellulosic paper and paperboard products such as file folders and paperboard file containers are often subject to liquid or moisture damage during routine handling and long term storage. In addition, such products, if stored in a humid environment, tend to support biological growth which results in undesirable odors being produced. Furthermore, such products may be damaged or soiled by aqueous liquids thereby discoloring the paper or paperboard products. If moisture or aqueous liquid are absorbed by the paper or paperboard materials, the materials may become soggy, warped and/or weakened thereby reducing their usefulness and potentially allowing the liquids to contact and damage documents which may be stored in containers made with the paper or paperboard materials.
Accordingly, there exists a need for improved cellulose-based products, and in particular relatively heavy weight paper and paperboard products, which exhibit improved resistance to moisture, water, and/or microbial growth.
With regard to the above and other objects and advantages, the invention provides a method for increasing the long term storageability of a cellulosic paper or paperboard product. The method includes providing a paper or paperboard product made from cellulosic fibers having a basis weight ranging from about 80 to about 300 pounds per 3000 square feet. A holdout material is applied to at least one surface of the paper or paperboard product to provide a sized web of paper or paperboard. The sized web is then coated with an ink receptive material selected from the group consisting of an aqueous acrylic polymer coating material, an aqueous biocidal agent and a combination of aqueous acrylic polymer coating material and aqueous biocidal agent to provide an ink receptive layer. Then the web is dried at a first temperature to provide a coated web. In order to reduce web curl, an uncoated side of the web is wetted with an aqueous fluid and dried at a second temperature to provide a paper or paperboard product having enhanced long term storageability.
In another embodiment the invention provides a method for reducing microbial growth on stored paper or paperboard products. The method includes providing a paper or paperboard product made from cellulosic fibers having a basis weight ranging from about 80 to about 300 pounds per 3000 square feet. At least one surface of the paper or paperboard product is sized with from about 0.5 to about 1.5 percent by weight starch sizing agent to provide a sized web of paper or paperboard. The sized web is coated with an aqueous biocidal agent and the web is dried to provide a paper or paperboard product having reduced tendency for microbial growth.
Another embodiment of the invention provides a paper or paperboard composite having enhanced long term storageability. The paper or paperboard composite includes a base layer formed from a cellulosic fiber substrate, the base layer having a first surface, second surface and a basis weight ranging from about 80 to about 300 pounds per 3000 square feet. A holdout layer is applied adjacent the first surface of the base layer. An ink receptive coating material is applied adjacent the holdout layer to provide an ink receptive layer. The ink receptive coating material is selected from the group consisting of an aqueous acrylic polymer coating material, an aqueous biocidal agent and a combination of aqueous acrylic polymer coating material and aqueous biocidal agent.
An advantage of the invention is that relatively heavy weight paper and paperboard products may be stored for a long term without significant deterioration or production of odor causing organisms. The products of the invention also exhibit improved long term durability and resist damage and staining caused by water and other aqueous fluids. Another advantage of the invention is that paper and paperboard webs made according to the invention exhibit less tendency to slide relative to one another as compared thermoplastic coated webs which are difficult to stack on one another because of their slick surface.